Purification of butadiene



Patented Nov. 28, 1944 UNlTED STATES PATENT orrics 2,353,527PURIFICATION OF BUTADIENE Lee H. Horsley and Howard S. Nutting, Midland,

Mich., assignors to The Dow Chemical Company, Midland, Mlch., acorporation of Michi- No Drawing. Application October 31, 1941,

Serial No. 417,313

Claims.

This invention relates to a method for Purifying 1,3-butadiene and moreparticularly to a method for separating therefrom alpha-acetylenes whichtend to distill with it and which have the general formula:

ene, butylenes, amylenes, etc.; dioleflnes such as butadiene, isoprene,hexadienes, etc.; and acetylenic hydrocarbons such as acetylene,methylacetylene, ethyl-acetylene, vinyl-acetylene, etc. The number andkinds of hydrocarbons in the pyrolysis mixture are dependent, of course,on the hydrocarbon materials subjected to the pyrolysis and theconditions under which the pyrolysis is carried out.

Economical methods are known whereby such complex mixtures ofhydrocarbons may be separated into fractions consisting in someinstances of only a single hydrocarbon and in others of only a few ofthe more closely related hydrocarbons in the original pyrolysis mixture,but certain of the fractions thus obtained comprise two or morehydrocarbons which are so closely related as regards certain of theirphysical and chemical properties that separation of the same by usualpurification methods is diillcult and impractical.

For instance, cracked-oil gas, which often contains all of thehydrocarbons above-mentioned, may be fractionally distilled to obtainfractions consisting substantially of hydrocarbons having the samenumber of carbon atoms in the molecule, e. g., a fraction consisting ofbutane, butylenes, butadiene, ethyl acetylene, and vinyl acetylenetogether with minor proportions of methyl acetylene and isoprene.However, the hydrocarbons in such fraction tend to distill together andfurther separation by distillation is not readily attained. Theacetylenes an the conjugated diolefines in particular are difflcult toseparate from one another. It is an object of this'invention to providea method whereby such hydrocarbons, i. e., acetylenes and conjugateddioleflnes,'may be separated. A particular object is to provide suchmethod whereby the acetylenic hydrocarbons, which are usually present insmaller amounts than the dioleflnes, may preferentially be dissolved outof the hydrocarbon mixture with a suitable solvent. We have discoveredthat when a gaseous or liquid hydrocarbon mixture comprising aconjugated diolefine and an alpha-acetylene, each having from three tofive carbon atoms, inclusive, in the molecule, is brought into intimatecontact with, or scrubbed by, water the alpha-acetylene is separatedleaving the diolefine substantially free of alphaacetylenes. Otherhydrocarbons, e. ,g., olefines or parafllns, if present in thehydrocarbon mixture remain largely undissolved togetherwith thediolefine.

The treatment of the hydrocarbon mixture with water may be carried outconveniently and in continuous manner by passing the mixture through ascrubbing tower, column, extraction chamber,

or other suitable contacting chamber in countercurrent relationship withwater. If desired, the

water may be treated previous to the extraction to free it fromdissolved gases such as air and carbon dioxide to avoid introducingthese substances into the extraction system. The water may also betreated to remove dissolved salts such as those of calcium and magnesiumwhich, ii? present in appreciable amounts, may lead to the formation ofundesirable solid deposits. The hydrocarbon mixture is preferablyintroduced in gaseous or vaporized form to the treatment, but it'maysatisfactorlly be treated while in liquefied form, provided care istaken tobring the mixture into intimate contact with the water used asthe extractant.

Scrubbing of the gaseous phase is usually carried out at a temperaturebetween 0 and 150 C. and preferably be tween 0 and C. The pressure ispreferably regulated to slightly below that at which the higher boilingof the major components of the hydrocarbon mixture is liquefied at thetemperature at which the treatment is carried out. The maximumsolubility of the components of the gaseous scrubbed per unit of time ina given column will be decreased and the amount of water used per unitof mixture treated will be increased. Al-. though the optimum amount ofwater depends,

hydrocarbon mixture in the to reduce the acetylene content of thehydrocar bon gases to any desired degree. There is a very little heatefiect occasioned by the contacting of the water with the gaseoushydrocarbons, and the treating temperature is usually controlled bypumping both the water and the hydrocarbon mixture to the column, whileat the desired temperature.

After such gaseous phase scrubbing to remove the alpha-acetylenes, thediolefine, e. g., butadiene, is, of course, saturated with water vaporand also contains the major portion of any saturated hydrocarbons, suchas propane or butane, which may be present in the hydrocarbon mixturebefore treatment with water. If necessary, it may be dried and furtherpurified in 'known ways. The eiiluent water contains the alphaacetylenestogether with minor amounts of the I conjugated dioleflne. Unsubstitutedacetylene and any minor amounts of carbon dioxide, sulfur dioxide andother water-soluble gases are also mostly removed by the treatment withwater as are also smaller amountsof higher unsaturated hydrocarbonswhich may be present in the untreated hydrocarbon mixture.

The degree of separation of the hydrocarbon mixture may be increased byremoving a part of the dissolved gases from the eilluent water, e. g.,by reducingthe pressure or by heating, and recycling the evolved gasesthrough the scrubbing column. Such recycled gases are rich in acetylenesas compared with the untreated mixture I and are usually fed into thelower portion of the .maining dissolved gases, e. g., methyl acetylene,

ethyl acetylene, vinyl acetylene and minor amounts of 1,3-butadiene.

As hereinbefore mentioned. the hydrocarbon mixture may be treated whilein liquefied form with water to extract alpha-acetylenes therefrom. Suchliquid phase extraction may be carv ried out in suitable equipment atany pressure sufllcient to liquefy the hydrocarbons and with agitationor addition of chemical dispersing agents, or other provision forobtaining rapid and intimate contact with the water. Otherwise, theextraction of the hydrocarbons in liquefied form is carried out underconditions similar to those employed in extracting the vaporizedhydrocarbuns with water. It is because of the inconvenience-involved ineffecting such intimate contact between the liquid hydrocarbon mixtureand the water that we prefer to scrub the hydrocarbons while invaporized form.

The following example will serve to illustrate the principle of theinvention, but is not to be construed as limiting its scope:

EXAMPLE A number of experiments were carried out wherein crude gaseous1,3-butadiene containing 85.4 per cent butadiene, 4.7 per cent ofalphaa/cetylenes, and 5.1 per cent higher boiling hydrocarbons wasscrubbed in continuous manner with water in a column 4 inches indiameter by 30 feet long packed with Raschig rings. The butadiene wasvaporized, warmed to the scrubbing temperature, and fed into the columnsix feet from the bottom. The water was warmed to approximately the sametemperature as the butadiene and fed into the top of the column. Thepressure on the column was maintained at slightly below the liquefyingpressure of butadiene at the temperature of the experiment. The pressureon the eiliuent water was reduced to an absolute pressure of 15 to 20inches of mercury and the gases thus recovered from the water werecompressed and returned to the bottom of the column. The remainingdissolved gases, consisting largely of acetylenes together with a minoramount of butadiene were discarded with the waste water after collectionof a sample for analysis. The scrubbed butadiene was collected and,while under pressure, was liquefied by cooling. The accompanying tablelists the data collected during the course of the experiments.Percentages given are by weight.

Table Experiment No.

Crude butadiene: Lbs. treated per hour l. 65 2.05 l. 71 3. l8 3. 0Treating conditions in colum Temperature (C.) 33 34 44 55 52 Pressure(Lb. gauge)" 29 32 48 60 55 Lb. water used per hour 380 362 360 m0 615Purified butadleno:

Per cent recovery 94 89 93 96 Per cent alpha-acetylcnes 0. 05 0.1 0. 050. 4 0. 05 Per cent high boiling hydrov carbons 0.9 i). 9 Recycled gas:

Per cent alpha-acetylene... 20 20 i7 18 Lb. gas recycled per hour Nonel. 0 l. 25 l. 25 Waste water: Per cent alphaacetylenes in dissolved gas78 64 61 1 Practically quantitative.

By a procedure similar to that illustrated in the foregoing example,isoprene may be freed from the acetylenic impurities often incident toits manufacture.

Other modes of applying the principle of the invention may be employedinstead of those explained, change being. made as regards the processherein disclosed, provided the step or steps stated by any of thefollowing claims or the equivalent of such stated step or steps beemployed.

We claim:

1. The method of separating alpha-acetylenes from hydrocarbon mixturescontaining the same in admixture with conjugated diolefines, each havingless than 6 carbon atoms in the molecule, which comprises scrubbing thehydrocarbon mixture at a temperature below C. with a volume of watersumcient substantially to dissolve the alpha-acetylenes, and separatingthe residual hydrocarbons from the aqueous extract.

2. The method according to claim 1, in which the scrubbing is carriedout at superatmospheflc pressure below that at which any of thehydrocarbons are liquefied at the temperature employed.

3. The method according to claim 1, in which the alpha-acetylenes in themixture are from the group consisting of methyl acetylene, ethylacetylene, and vinyl acetylene, and the conjugated diolefine is1,3-butadiene.

4. The method of separating alpha-acetylenes 10 from hydrocarbonmixtures containing the same in admixture with coniugated diolefines,each having less than 6 carbon atoms in the molecule, which comprisesscrubbing the hydrocarbon mixture in countercurrent manner at a tempera-15 ture below 150 C. with a volume of water sumcient substantially todissolve the alpha-acetylenes, separating the residual hydrocarbons fromthe aqueous extract, vaporizing at least a portion of the dissolvedgases from the aqueous extract and returning such gaseous portion to thescrubbing' step at a point below that at which the original hydrocarbonmixture is introduced.

5. The method according to claim 4, in which the alpha-acetylenes in themixture are from the group consisting of methyl acetylene, ethylacetylene and vinyl acetylene, and the conjugated dioleflne is1,3-butadiene.

LEE H. HORSLEY. HOWARD S. NUTTING.

